A variety of illnesses manifest themselves through periodic and recurrent episodes of various symptoms. Many of these symptoms are amenable to monitoring through the use of various kinds of machinery. Although the further description of the present invention and its background is made with reference being had mainly to the condition of angina pectoris, it is to be understood that the invention is not restricted to this particular use, but its scope is determined by the claims.
In studying the effect of anti-anginal drugs, one must be aware of the mind set of the Food and Drug Administration and of the expert committees on which it relies in the approval process for such drugs. Anginal pains can be brought on by physical exercise In studying new anti-anginal drugs one primary indicator is the ability of the patient to increase the duration of an exercise between medications, where the increase is brought about by a drug that is being investigated. Thus, the duration of exercise is compared in the case of taking the medication under investigation, with the use of a placebo and/or with a standard reference anti-anginal drug such as propranolol. A patient suffering from angina condition will tolerate only a certain amount of exercise before the onset of the pain. In the case of standard reference anti-anginal drugs the period by which the onset of the pain can be delayed has been well established. The effect of an experimental drug to prolong the exercise period before the onset of pain can, therefore, be compared to the effect without medication, or to when a standard referenced drug is taken. This "exercise-tolerance test" is a difficult, time consuming, and expensive test and, moreover, may not be adequately representative of the actual life conditions under which angina patients exist and for which anti-anginal drugs are intended. Moreover, angina attacks can also occur in the absence of physical exercise, due to emotional stress or other factors which are not addressed by the exercise-tolerance test. Therefore, researchers have employed alternative methods for measuring the efficacy of experimental anti-anginal drugs.
An alternative method involves administering a standard dosage of the experimental anti-anginal drug at standardized intervals of time The patient is permitted to take nitroglycerin tablets between administrations of the experimental drug, whenever angina pain occurs. The reduction of nitroglycerin intake compared to a standardized level of such intake is another indication of the efficacy of the experimental anti-anginal drug. However, exercise tolerance testing is considered by the regulators to be the most important proof of efficacy. Therefore, even if a significant reduction in nitroglycerin consumption can be shown but there is no increase in exercise tolerance, then the new drug would usually not be approved under contemporary acceptance standards of the FDA.
Another method employed by researchers is a handwritten diary by patients recording the date and time of anginal episodes. The FDA and its expert panels are generally reluctant to accept patient diaries, because they were always suspicious about their reliability. It was felt that patients do not start to make handwritten entries into a diary when they experience pain and are just as unlikely to record in writing accurately the end of the pain episode.
Particular difficulties arise in testing the effect of continuously administered nitrate products intended to prevent or reduce the frequency of angina attacks. When exercise tolerance testing is employed, the results can suggest that the active ingredient, as measured by this method, may lose its activity. Tolerance will develop in some patients when nitrate products are administered continuously. At the same time patients do not complain of an increased frequency of episodes. An uncertainty is introduced into the evaluation, because the investigator does not know whether the loss of effect shown by exercise-tolerance testing is realistic, i.e. whether the loss of effect is a phenomenon of the testing system but does not portend lack of effect under the patient's actual lifestyle conditions. Therefore, the exercise tolerance testing may also not really reflect the realities of day-to-day life.
It became clear from the foregoing considerations that a simple device by which angina attacks could be assessed under actual living conditions of patients, would be an ideal way of evaluating anti-anginal drugs, but the prior art which was reviewed provided no guidance in that direction.
U.S. Pat. No. 4,518,267 discloses an event-module for the measurement and study of times, intervals, period, time series and durations. It is a complex device recommended for the treatment of addicts, such as smokers, alcoholics and over-eaters The device is meant to be a therapy support in assisting the patient to fight his habit, rather than a means of diagnosing or evaluating the incidence, severity, and other medical information pertaining to a medical condition such as, for one example, angina. The device is meant to divert the thoughts of the patient by providing him with a game to play. The patient can also enter times and durations of sporting events which he watches, further to divert his attention from his addiction.
U.S. Pat. No. 4,686,624 discloses an apparatus for acquiring and processing data on the dietetics and/or health of a person. The apparatus contains alphanumeric keys for inputting information, window for displaying the information that was introduced and various indications relating to them on the basis of pre-programmed parameters, and a device for selectively refusing inputs. On the basis of the inputs a computer generates instructions for the user of the apparatus from a program, such as what kind of food to eat, or medications to take. The device of the present invention is intended for the purpose of accurately recording patient-generated information pertaining to self-recognized symptoms of a known or suspected disease (e.g. angina pectoris) to facilitate physician or investigator evaluation of the patient's medical condition or response to treatment, under the patient's normal conditions of living.
U.S. Pat. No. 4,653,022 discloses a portable electrocardiogram storing apparatus, a patient actuatable switch, a plurality of electrocardiogram memories, and means for selecting when the switch is actuated, one of the memories for storing the digital signal of an electrocardiogram. The storage also contains timing signals relative to when the cardiogram was taken and stored. The primary purpose of this device, however, is to store information about clinical signs, which may or may not be apparent to the patient.
Also known is a device under the name of Holter monitor. This is a simplified electrocardiographic sensor which provides a single lead tracing over a prolonged period of time. Therefore, it provides a snapshot, as is the case with electrocardiograms. The Holter monitor is designed for recording the onset and frequency and duration of ischemic events, but these do not necessarily correlate with symptomatic angina. The ischemic phenomenon of "silent angina", in which the electrocardiographic changes typical of angina are present but without all the symptoms of an angina attack, is well documented. In such cases electrocardiographic tracing has no corollary in any patient-sensed symptoms, i.e. the patient feels no pain or onset of attack. Furthermore, the Holter monitor does not provide a means for recording the severity of the attack. Another purpose of the Holter monitor is to record electrocardiographic signals over time to track heart arrhythmias, many of which are, like silent angina, not symptomatically apparent to the patient. Furthermore, it is a magnetic recording rather than a graphic strip.